Neutering is removal of the testicles or ovaries. Castration is removal of the penis.
Body modification (or body alteration, called body mutilation by detractors) is the deliberate altering of the human anatomy or phenotype. It is often done for aesthetics, sexual enhancement, rites of passage, religious beliefs, to display group membership or affiliation, to create body art, for shock value, and as self-expression, among other reasons. In its most broad definition it includes plastic surgery, socially acceptable decoration (e.g., common ear piercing in many societies), and religious rites of passage (e.g., circumcision in a number of cultures), as well as the modern primitive movement.
In contrast to the explicit ornaments, the following procedures are primarily not meant to be exposed per se, but rather function to augment another part of the body, like the skin in a subdermal implant. Cybele
In ancient civilisations, removal of the human penis was sometimes used as a means of demonstrating superiority: armies were sometimes known to sever the penises of their enemies to count the dead, as well as for trophies. The practice of castration (removal of the testicles) sometimes also involves the removal of all or part of the penis, generally with a tube inserted to keep the urethra open for urination. Castration has been used to create a class of servants or slaves (and especially harem-keepers) called eunuchs in many different places and eras.
In the modern era, removal of the human penis is very rare (with some exceptions listed below), and references to removal of the penis are almost always symbolic. Castration is less rare, and is performed as a last resort in the treatment of androgen-sensitive prostate cancer. Penis